During the processing of metals in their molten state, it is necessary to obtain a representative sample of the molten metal at various stages of the process, for example, for the analysis or evaluation of either the chemical composition or the metallographic structure of the metal sample. Different methods for analyzing molten metals (particularly steel) during manufacturing and further processing are known in the art. For example, German Patent No. DE 3344944 discloses a method for analyzing steel during its manufacture and further processing. The method is characterized by the following steps which are carried out consecutively: (1) magazineing a sampling lance and automatically pre-selecting the sample type; (2) collecting a sample of molten steel during the blowing phase in a converter or an electric furnace from a control stand; (3) unpacking the sampling lance and disposing of its cardboard and ceramic parts in an unpacking machine; (4) comparing the mass of the sample with a specified value for the purpose of early fault detection; (5) passing the sample through a cooling section supplied with water, air, inert gas and dry ice; (6) conveying the sample with the aid of a cartridge by means of a pneumatic tube conveyor section having an automatic sending and receiving station; (7) preparing the sample for spectral analysis in an automatic sample polishing machine; (8) detecting faults in the polished steel samples and documentation of the defects; (9) transferring the steel sample to the Petri stage of a spectrometer using a manipulator; (10) analyzing the sample in the spectrometer; and (11) communicating the analytical data to the control stand. In a typical steelmill, some of the above steps are manual and others robotic. However, the entire analytical process is time consuming and labor intensive.
Conventional sampling devices (e.g., the sampling lance of German Patent No. DE 3344944) to extract samples from a molten metal bath are also known from published patents and patent application. Other conventional sampling devices, which are not the subject of a patent or patent application, are known, for example, due to their availability on the market. These conventional sampling devices or samplers generally provide a coupon or disc of solid metal for use in spectrographic and metallographic analysis.
The geometric shape and dimensions of the solidified metal coupons obtained by such sampling devices will sometimes be specific to the type of metal or metallographic need. However, a general category of samples that are obtained by immersion devices are samples having a disc or oval shape and a diameter or long length of 28-40 mm. Most commonly, such samples have a diameter or long length of about 32 mm and a thickness of 4-12 mm. Some samplers, commonly known as lollipop samplers, may produce a differently shape sample, ranging from round to oval or longer, according to the requirements of the user, but most samples still have a diameter or long length of about 32 mm.
Other samplers, commonly known as dual thickness samplers, combine two thicknesses within the same sample. For analysis of the dual thickness samples, the 12 mm section is the portion which is spectrally analyzed. It has been found that a solidified sample of this thickness requires surface grinding from 0.8 to 5 mm in order to achieve an analysis surface which is free from metal and non-metallic segregation. Eliminating the need for surface preparation would speed the analysis time and would economically be favorable. However, this would only be achievable by a uniform filling of the sample cavity with molten metal and rapid chilling of the molten metal sample, such that the entire sample section freezes uniformly.
Typical sampling devices include a sample chamber or mold cavity configured to be filled with molten metal upon immersion of the sampling device into the molten metal bath. The molds which delineate the mold cavity or sampling chamber are typically either a two-part clam shell type arrangement or a ring covered on its upper and lower sides by flat plates. U.S. Pat. No. 3,646,816 describes this type of expendable immersion sampler, in which both flat surfaces of a disc-like sample are formed by chill-plates to achieve more rapid freezing and a pair of smoother surfaces which require less clean-up prior to analysis. Other prior art patents, such as U.S. Pat. No. 4,211,117, relate to a similar concept, while U.S. Pat. Nos. 4,401,389 and 5,415,052 provide examples of this metallurgical sample being combined with other sensors, one of which could be a temperature measuring sensor.
Historically, in all but a limited number of circumstances, the solidified metal sample obtained at a metallurgical process location is physically transported to a remote chemical laboratory, where the composition of the solidified metal sample is often determined using arc spark-optical emission spectroscopy equipment. Optical emission spectroscopy (or “OES”) systems are generally the most effective systems for determining the chemical composition of a metal sample and for controlling the processing of molten metals due to their rapid analysis times and inherent accuracy. The results of this analysis are then returned to the metallurgical process location where the attending operators utilize those results to make decisions regarding further processing. Broadly speaking, the OES analysis procedure begins with the conductive metal sample being positioned with its analysis surface face down on a predetermined region of the stage of the OES instrument, namely an optical emission spectrometer. More particularly, the sample is positioned so as to span and close the analysis opening of the spectrometer and an anode nearly abuts the analysis surface of the sample. Once the desired positioning of the sample and proximity of the anode and analysis surface is achieved, a spark is discharged between the anode and the conductive metal sample which is electrically connected to the spectrometer stage. This connection is, in most cases, made by gravitational force in combination with a small load. The analysis opening on the optical emission spectrometer is typically around 12 mm wide. This distance avoids that a spark arcs between the anode and the instrument housing. The optical detector receives the emitted light from the excavated material of the sample surface. The spark chamber, formed in part by the space between the anode and the metal sample, is continuously purged with argon or other inert gas in order to avoid air ingress which would lead to erroneous analysis values.
In order to lay flat across the analysis opening of the spectrometer, the metal sample cannot have any extensions and the analysis surface of the metal sample must be smooth (i.e., of there can be no parts of the sample housing which break the plane of the analysis surface). The sample must span the analysis opening of the spectrometer and be of sufficient flatness to facilitate inert gas purging of the spark chamber and present a contiguous sample surface toward the anode.
It has been demonstrated that when placing such analytical equipment in a factory environment, near the metallurgical process location, more timely results are obtained and significant cost savings can be gained by eliminating transport and handling efforts. There are several problems associated with providing a metallurgical sample for these types of local analytical systems, as well as some prior art solutions for these problems. For example, it has been found that exposing the hot metal surface of the solidifying or solidified sample to atmosphere will quickly result in the formation of oxides on its surface, which must be later removed by mechanical grinding in order for the sample to be analyzed by OES. One solution to this problem has been to remove the heat of the solidifying metal to bring the metal sample to near room temperature before it is removed from the sample chamber.
Direct Analysis (DA) samplers are a newly developed type of molten metal immersion sampler which produce DA samples. DA samples do not require any kind of surface preparation before being analyzed, and thus can result in significant economic benefit both in terms of the availability of timely chemistry results as well as laboratory time savings by utilizing the OES analysis method.
U.S. Pat. No. 9,128,013 discloses a sampling device for retrieving a rapid chilled sample from a converter process for making steel that is intended for local analysis. The sampling device includes a sample chamber formed by at least two parts, where the specified ratio of the mass of the melt taken up in the sample cavity to the mass of the sample chamber assembly enables a rapid cooling of the melt filling the sample cavity. When this sample chamber is removed from the measuring probe, thereby exposing the sample surface to atmosphere, the melt has already cooled sufficiently that oxidation is prevented to the greatest extent possible, and therefore post-treatment of the sample surface is unnecessary.
A similar DA type sampler is known from U.S. Patent Application Publication No. 2014/318276. One end of the sample cavity of this DA type sampler is connected to the molten metal bath during immersion of the sampler via an inflow conduit, while an opposite end of the sample cavity is in communication with a coupling device. During immersion, but before the filling of the sample cavity with the molten metal, the sample cavity is purged with an inert gas to avoid early filling and oxidation of the sampled material. The inflow conduit is arranged perpendicular to the flat surface of the sample cavity. The ventilation of the sample cavity is arranged below the analysis surface of the sample cavity relative to the immersion direction.
The above-described sampling device is meant to be used in steelmaking processes, specifically in a converter application. Steel samples and steel bath temperatures are measured either from the tilted converter after interruption of the blow or by means of special equipment called a sublance, according to U.S. Patent Application Publication No. 2014/318276. In the latter case, the converter can stay upright and the blowing process can continue, thus saving time. The oxygen steelmaking process aims to achieve precise end point values for steel weight, temperature and composition. Carbon, phosphorus and sulphur concentration and, in some instances, special elements detrimental to the final steel properties are monitored for their content in the steel to be within compositional target windows. A fast analysis DA type sampler can provide the confirmation of the composition in much less time than a conventional sampling device, since the analytical procedure is reduced to de-molding the solidified sample, transferring the sample to a spectrometer and placing the sample on an OES stage for analysis.
In converter applications, the oxygen content of the steel is considered high. In particular, at the end of the oxygen blowing process, the oxygen content of the steel is typically on the order of 500-1000 ppm. A sample taken from this bath would cool and expel carbon monoxide when the decreasing temperature of the steel (i.e., during cooling) exceeds the oxygen solubility for that temperature and its carbon content. These gas bubbles lead to an irregular surface and a hollow sponge like structured sample. To avoid this problem during cooling, prior art samplers, such as those described in U.S. Pat. Nos. 4,037,478 and 4,120,204, are provided with a deoxidant, most commonly aluminum and zirconium. However, a rapidly filled DA sampler with a small cross section and rapid chill sample chamber has been shown to result in a poor distribution of the deoxidant as the section of the sample decreases, thus establishing a limitation to reduction of the sample volume.
Thus, there is a need to provide a means for mixing deoxidizing materials into rapid chill samplers to obtain an improved distribution.
Also, samples produced by conventional sampling devices have a diameter of at least 32 mm in a direction parallel to the spectrometer opening and a thickness of 4-12 mm in a direction perpendicular to the spectrometer opening. Such dimensions can be easily handled by pre-analysis preparation equipment that mechanically grinds the analysis surface of the metal sample to clean oxides from the surface and provide the requisite flat topography. This geometry is also convenient to robotic manipulators which advance the sample from preparation through analysis and removal to await the next sample. Robotic equipment in a typical steelworks laboratory is difficult to modify to accept radically different sample geometries.
However, the prior art sample volume is over dimensioned from the minimum volume of metal required to arrive at the minimum necessary analyzed surface area. The sample volumes of the prior art devices thus preclude rapid solidification of the molten metal sample, which is necessary to obtain an oxide free surface. As such, conventional devices cannot be reliably analyzed by OES without surface preparation. Using massive cooling plates and sampler housings to force a large volume metal sample to low temperature after retrieval becomes impractical for rapid de-molding and is uneconomical for use as immersion sampling devices.
Accordingly, it would be beneficial to provide a DA type sampler which produces preparation free samples of deoxidized steel from a converter or other processing vessel that are capable of rapid chilling as necessary for obtaining an analysis surface which is free from metal and non-metallic segregation which can be analyzed by OES.
It would also be beneficial to provide a DA type sampler, particularly one which is adaptable for use in sampling molten steel, which produces a DA type sample capable of being analyzed on existing OES equipment, thereby improving the speed and accuracy of the analysis.
It would also be beneficial to provide a molten metal immersion device for retrieving preparation free samples from a molten metal processing vessel which is capable of quick connection to pneumatic-assisted inert gas purge apparatus and exhibits reduced pressure metal uptake. In particular, it would be beneficial to provide a molten metal immersion device for producing a molten metal sample that is easily obtained and quickly removed from the immersion device housing, de-molded from the sample chamber, and directly analyzed on the OES without additional cooling or preparation, and which is thereby cost-effective.